Clamping roller freewheels are a special type of the range of freewheel devices referred to generally as clamping body freewheels. Said clamping roller freewheels are used for example as overrunning clutches which, for example, decouple an originally driven branch of a drivetrain when said branch overruns the driving part of the drivetrain. Freewheel devices of said type are also used as non-return devices. The functional principle of all clamping body freewheels is that, in one drive direction, the clamping bodies become wedged and thereby produce a force-fitting connection between the inner ring and outer ring, while in the other drive direction the wedging action is eliminated and the inner ring is thereby decoupled from the outer ring.
A distinction is made fundamentally between clamping roller freewheels with clamping ramps formed on the inner ring (inner star) or clamping ramps formed on the outer ring, with the drive generally being introduced via the ring which has the clamping ramps. The former clamping roller freewheels have the advantage over the latter type that the centrifugal forces acting on the clamping rollers assist the clamping action, that is to say the abutment against the outer ring, while in the latter type the centrifugal force counteracts the clamping action. For this reason, clamping roller freewheels, which are used as overrunning clutches, are usually formed with an inner start. At relatively high rotational speeds of the inner ring in idle running operation, the clamping rollers are pressed against the outer ring by centrifugal forces, such that friction forces are generated between the clamping rollers and the outer ring.
One difficult aspect in structural terms is that of optimally designing the clamping springs which preload the clamping rollers in the direction of their clamping position and which likewise press the clamping rollers against the outer ring. If the clamping springs are too strong, then, in overrunning operation, the outer ring grinds against the clamping rollers, which leads to wear of the clamping rollers. In contrast, if the clamping springs are too soft, the clamping rollers are driven by the outer ring in overrunning operation. The wear is thereby relocated to the clamping ramps on the inner ring or to the clamping springs. So-called idle running wear generates an increase in the clamping ramp angle and, therefore, a reduction in the slip resistance of the freewheel. A rotational movement of the clamping rollers in overrunning operation can also have the result of changing the position of individual clamping rollers on the associated ramps, such that these are overloaded when the freewheel switches to driving operation. This may result in plastic deformation of the ramps and even in the clamping rollers overrunning the ramps.
DE 1 706 448 U1 has already disclosed a clamping roller freewheel of the type specified in the introduction, in which, in the freewheeling or overrunning position, the clamping rollers are pulled against the wedge surface star by means of a resilient tension element, which is wrapped around all of the clamping rollers, such that said clamping rollers do not make contact with the outer ring (referred to as the clamping ring), that is to say said clamping rollers are lifted up from said outer ring entirely. In this way, no tangential force is transmitted from the outer ring to the clamping rollers in this operating state, such that a switch to driving operation does not take place immediately upon the synchronization of the speeds of the inner ring and outer ring, but rather only when a predefined rotational speed of the inner ring is reached at which the clamping rollers are adjusted by centrifugal force into an initial clamping position, which then leads to wedging of the clamping rollers.